Abstract

The rate of inorganic carbon (Ci) uptake and RuBisCO activity
was examined in batch culture, in a range of unicellular
cyanobacteria grown under different carbon regimes. There was no
significant increase in RuBisCO activity seen in CO2-limited
cultures. All of the species capable of growth in freshwater
were found to possess, to varying degrees, an active, saturable,
mechanism for the transport of Ci. Three oceanic, phycoerythrin
containing unicellular cyanobacteria did not possess a Ci uptake
mechanism following growth under high and low CO This may be
related to the nature of the environment which these organisms
inhabit.
Addition of sodium bicarbonate and glucose to low CO2-grown
Synechocystis PCC6803 resulted in a rapid decay in Ci uptake,
with a t0.5 for the decay of 1.15 h. Addition of the
non-metabolizable glucose analogues 3-0-methyl-D-glucase (OMG)
and 2-deoxy-D-glucose to low CO2-grown Synechocystis PCC6803
resulted in different effects on the cells ability to transport
Ci. Addition of OMG resulted in no significant decline in the Ci
uptake mechanism, whereas addition of DOG led to a similar decay
in Ci uptake to that seen following addition of glucose. From
these results it is suggested that the different structures of
the analogues are responsible for the differences seen, and that
build-up of a pool of glucose-6-phosphate is a signal for the
inactivation of the Ci uptake mechanism in Synechocystis
PCC6803.
Examination of the Ci uptake mechanism and RuBisCO activity in
DIC and light-limited chemostats of Synechococcus PCC7942
resulted in the finding that cultures which were DIC-limited for
growth were not DIC-limited with respeqt to the Ci uptake
mechanism. RuBisCO activity increased in three distinct stages
as the external DIC concentration fell. The 42 kD cytoplasmic
membrane polypeptide was present in organisms isolated from
DIC-limited chemostats with no appreciable Ci uptake mechanism.
The in vivo and in vitro phosphorylation pattern of
Synechocystis PCC6803 was also examined in response to growth
under different carbon regimes. Low CO2-grown cultures contained
few phosphopolypeptides. Addition of sodium bicarbonate and
glucose to low CO2-grown cells led to the appearance of a number
of phosphopolypeptides over a similar time course seen to the
decay of the Ci uptake mechanism. The glucose analogues DOG and
OMG had no effect an the phosphorylation pattern in low
CO2-grown cells. In vitro kinase experiments an cell-free
extracts resulted in a number of polypeptides becoming
phosphorylated, some corresponding on SDS-PAGE to those seen in
vivo. The in vitro phosphorylation pattern could be requiated by
altering the redox potential and addition of RUBP.
At the molecular level, the construction and use of the lacZ
promoter probe pLACPB2 led to the identification of a number of
presumptive CO2-regulated promoters.